DE4010285C2 - - Google Patents

Description

The invention relates to an electrochromic device according to the preamble of Claim 1.

Such an electrochromic device is for Prussian blue from US 47 73 741 or also from US 48 01 195 known. From Derwent Abstract 86-0 38 214/06 is known to be Prussian blue, ruthenium purple and osmium purple can form electrochromic layers. The mixture of the transition table according to claim 1 with gold is neither from US 47 73 741 nor from US 48 01 195 known.

Conventional electrochromic materials (EC materials) are divided into two types, these as "oxidation type" or referred to as "reduction type" in the following. An oxidation type EC material takes color in its electrochemically oxidized state while a reduction type EC material has a color in it electrochemically reduced state.

DE 34 38 492 11 A1 relates to an EC device, preferably two layers of Prussian blue the opposite electrodes can be used. An alkali salt is preferred as the electrolyte solution LiClO₄, NaClO₄ or KBF₄, in an organic polar Called solvent.

From the SP-A-58-2 15 630 in Patent Abstracts of Japan, Vol. 8, No 68 (P-264) March 30, 1984 is an electrochromic Element known in which u. a. the Deterioration of the display characteristics should be prevented during storage. Electrolyte mixtures are used for this, the lithium and sodium ions at the same time contain.

It is known to combine EC material from Oxidation type and a reduction type EC material to be used in an EC device which is two opposite arranged electrodes. The two Types of EC materials are the two electrodes assigned. For example, JP-A 59-1 59 134 an EC display device using a combination of Prussian blue, which has a blue color adopts its electrochemically oxidized state and colorless through reduction, and from tungsten trioxide, which is colorless in its electrochemically oxidized state and assumes a blue color in a reduced state. Instead of Prussian blue, too Ruthenium purple can be used. In the EC device according to JP-A 59-1 59 134 is the space between the two opposite EC electrode layers with an electrolytic liquid  namely z. B. a solution of lithium perchlorate filled in propylene carbonate.

U.S. Patent 4,773,741 shows an EC display device with Prussian blue and tungsten trioxide. Instead of lithium perchlorate can also occur from sodium perchlorate. When operating the above EC display devices, the electrochemical oxidation of the EC material on an electrode of the electrochemical reduction of the EC material accompanied on the other electrode. Therefore, there is a simultaneous Discoloration of the two electrodes and a simultaneous Bleaching or becoming colorless of the two electrodes. The main purpose of this construction is intensification the blue coloring of the EC device with Prussian blue.

In the practical application of an EC device from It is not uncommon for the type described above that the EC device in the bleached state (i.e. the Prussian blue Electrode in reduced state) for several days or left for longer. If that's in one Condition of the EC device left discolored the density of the discoloration is less than that of the Discoloration process before the last bleaching process and in In some cases, it is even insufficient for practical ones Purposes. The discoloration density can vary to some extent can be achieved again by the discoloration and the fading is repeated many times, however it is for a full recovery of the discoloration density required, the EC device in a discolored state to be left for several days. This is the commercial one or practical value of the EC device.

Starting from an EC device according to the preamble of claim 1 Object of the present invention, to further develop this electrochromic device in such a way that she not a significant degradation or deterioration the discoloration density suffers even if the device is left in the bleached state.  

This object is achieved according to the characterizing part of claim 1 solved in that the electrolytic solution is a solution of lithium perchlorate and sodium perchlorate in the organic Solvent is, the sodium ions in the solution 3 to 30 mol% of the total amount of lithium ions and sodium ions turn off.  

The invention therefore lies in the combination specified above of cations in the electrolyte solution. It became too conclude that the degradation or Deterioration of the discoloration density caused by a Leave the EC device in a bleached or colorless Condition stems from a decrease in the amount of electricity in the electrochemical oxidation reaction of Prussian blue or an alternative EC material from Oxidation type in the EC device is attributable. The electrochemical oxidation and reduction reaction von Preußischblau can be represented by the following equation be, although the reaction mechanism is not yet has been fully clarified:

In the EC device according to US 47 73 741 using Prussian blue is the cation M⁺ the Li⁺ ion or the Na⁺ ion. There was now cation selectivity in electrochemical Oxidation reaction from Prussian blue to a quartz vibrator micro balance method in solution examined and found that in an organic polar solvents such as propylene carbonate affinity of Prussian blue for the Na⁺ ion about 15 times as high like that for the Li⁺ ion. However, if simple Na⁺ ions are used instead of Li⁺ ions, lowered the rate of the electrochemical reaction of WO₃ or an alternative transition metal oxide considerably on the opposite electrode, so that the EC device gets a low response.  

In the electrolyte solution used according to the invention the Na⁺ ion used together with the Li⁺ ion, where the amount of Na⁺ ions in the range of 3 to 30 mol% of Total amount of Na⁺ and Li⁺ ions lies. By using such an electrolytic solution will decrease the extent of the amount of electricity the oxidation reaction of Prussian blue or osmium purple or ruthenium purple from leaving the EC device comes in the bleached state, noticeably reduced, and therefore the discoloration density is next Staining process of the EC device sufficient, even if the device is bleached or for several days colorless condition was left. For example, in using an EC device according to the invention of Prussian blue and WO₃ the amount of electricity in the Prussian blue reaction initially about 15 mC / cm², and when this EC device is bleached for two or three days is left standing and then brought to oxidation, the amount of electricity is still so great such as about 12 mC / cm², d. H. more than 80% of the initial value. If the amount of Na⁺ ions in the electrolyte solution increases 1 or 2 mol% of the total amount of Li⁺ ions and Na⁺ ions is reduced, the amount of electricity will be about 70% of the initial value or even lower by leaving the EC device in the bleached, d. H. colorless condition for only 1 day.

The invention can be used in both EC display devices and also in EC plates or panels to control light transmission be exploited by this.

The invention is explained in more detail with reference to the drawing; are in the drawing  

Fig. 1 is an explanatory cross section Ec display device according to the invention and

FIG. 2 is a graph depicting the rate of decrease in the amount of electricity in an electrochemical discoloration reaction in an EC device of the type shown in FIG. 1, depending on leaving the EC device in the bleached state for a period of time, for one embodiment according to the invention and an embodiment in which only lithium is used.

Preferred embodiments are described in more detail below explained.

Fig. 1 shows the general structure of an EC display device. The EC display device has oppositely arranged front and rear substrates or supports 10 and 20 , both of which are transparent. A transparent electrode film 12 is deposited on the inner surface of the front substrate 10 , and a first EC layer 14 is formed on the electrode film 12 . Another transparent electrode film 22 is deposited on the inner surface of the back substrate 20, and a second EC layer 24 is formed on this electrode film 22 opposite to the first EC layer 14 . The transparent electrode films 12, 22 are usually made of SnO₂ and / or In₂O₃ using a PVD method such as by sputtering or vacuum evaporation (PVD = physical vapor deposition). The first EC layer 14 is made of an oxidation type EC material selected from Prussian blue, osmium purple, Fe (III) ₄ [Os (II) (CN) ₆] ₃ and ruthenium purple, Fe (III) ₄ [Ru (II) (CN) ₆] ₃, while the second EC layer 24 is formed of a transition metal oxide serving as a reduction type EC material selected from the group consisting of WO₃, MoO₃, V₂O₅, Nb₂O₅ and TiO₂ and mixtures thereof Oxides with gold.

The two substrates or supports 10 and 20 are separated from one another and arranged parallel to one another by means of a layer 30 of a sealing material which is applied peripherally to the substrates 10, 20 so that it surrounds the EC layers 14, 24 . Depending on necessity, tiny spacers such as glass spheres (not shown in FIG. 1) can be used to exactly define the distance between the two substrates 10 and 20 . The space formed between the two substrates 10, 20 is filled with an electrolyte solution 32 .

An auxiliary electrode 34 is arranged in an edge region of the intermediate space between the two substrates 10, 20 . The auxiliary electrode 34 is isolated from the transparent electrode films 12 and 22 , but it is ionically conductive with the electrode solution 32 . The main purpose of the auxiliary electrode 34 is to initially reduce the first oxidation type EC layer 14 . When the first and second EC layers 14, 24 are formed by the respective usual methods, it is inevitable that both of the EC layers 14 and 24 are in the electrochemically oxidized state, so that the first EC layer 14 (of the oxidation type) is theirs takes on characteristic coloring, while the second EC layer 24 (of the reduction type) remains colorless. It is therefore necessary to carry out the electrochemical reduction of the first EC layer 14 before the EC device is actually put into operation. The auxiliary electrode 34 is used for this reduction treatment. Furthermore, the auxiliary electrode 34 can be used to correct an imbalance in the electrical charges between the first and second EC layers 14 and 24 . The body of the auxiliary electrode 34 is usually formed from an electrically conductive material and a substance which is electrochemically and reversibly oxidizable and reducible. Reference numeral 40 shows a control device for supplying a controlled voltage between the two transparent electrodes 12 and 22 or between the auxiliary electrode 34 and one of the two electrode films 12 and 22 .

The electrolytic solution 22 is a solution of lithium perchlorate and sodium perchlorate in an organic polar solvent such as propylene carbonate, which is preferred, or acetonitrile. Optionally, a small amount of water (up to about 5% by weight) can be added to the organic solvent. The electrolytic solution 32 is prepared in such a way that the cations in the solution consist of 3-30 mol% Na⁺ ions and the rest of Li⁺ ions. If the amount of Na⁺ ions is less than 3 mol%, the influence of the addition of Na⁺ ions is not sufficient, so that the discoloration process of the EC device after leaving the device in the bleached or colorless state on one is not suffers from sufficient discoloration density. If the amount of Na⁺ ions exceeds 30 mol%, a considerably long period of time is required to bring about the bleaching of the EC device, in particular to bleach or become colorless of the transition metal oxide layer 24 and, in extreme cases, complete bleaching cannot be achieved. Preferably, the Na⁺ ions make up at least 5 mol% of the total amount of Na⁺ and Li⁺ ions, and in most cases an optimal amount of Na⁺ ions is in the range of 5 to 25 mol%.

example

An EC display device of the construction shown in FIG. 1 was produced using the following materials:

The transparent substrates 10 and 20 were glass plates with the dimensions 100 mm × 100 mm and a thickness of 1.2 mm. Each of the transparent electrode films 12 and 22 was an ITO film with a surface resistivity of about 20 Ω /. As the first EC layer 14 , a Prussian blue film with a thickness of about 400 nm (4000 Å) was produced by an electrodeposition method. As a second EC layer 24 , a WO₃ film with a thickness of about 400 nm (4000 Å) was produced by a vacuum evaporation method. Both the first and second EC layers 14 and 24 had an effective surface area of 60 cm². The body of the auxiliary electrode 34 was formed from a mixture of carbon, poly (4,4 ', 4''- triphenylamine) and a fluoroplastic (binder). The electrolytic solution 32 was a solution prepared by dissolving 0.8 mol of LiClO₄ and 0.2 mol of NaClO₄ per 1 propylene carbonate containing 1.2% by weight of water.

In this EC device, the layer 14 of Prussian blue initially had a blue color, while the WO 3 layer 24 was colorless. The Prussian blue layer 14 was left in a colorless and transparent state by an electrochemical reduction treatment using the auxiliary electrode 34 . Thereafter, a simultaneous discoloration of the Prussian blue layer 14 and the WO₃ layer 24 by applying a DC voltage between the two opposite electrodes 12 and 24 to the Prussian blue layer 14 to a potential of 1.0 V compared to the WO₃ layer 24 to hold, be brought about, and a simultaneous and complete bleaching or becoming colorless of the two EC layers 14 and 24 could be achieved by changing the potential of the Prussian blue layer 14 compared to the WO₃ layer 24 to 0.5 V.

Several samples of such an EC display device were left in the bleached state for various predetermined periods of time ranging from 1 day to more than 30 days. Thereafter, each sample was brought into a discolored state to measure the amount of electricity in the first discoloration reaction of the Prussian blue layer 24 , Q₂, after standing in the bleached or colorless state, and this value Q₂ was compared with the amount of electricity in the same reaction, measured before leaving the sample in the bleached state Q 1, compared. The results are shown in FIG. 2 by the solid curve I.

Comparison test

The EC device of the previous example was only modified in the composition of the electrolytic solution 32 . In this case, solution 32 was prepared by dissolving only 1.0 mol of LiClO₄ per 1 propylene carbonate, which contained 1.2% by weight of water.

Samples with the comparative test EC display device were subjected to the test described above to measure the speed of change in the amount of electricity in the discoloration reaction resulting from standing in the bleached state. The results are shown in FIG. 2 by curve II in a broken line.

In addition, the electrolyte solution of the comparative experiment was modified by replacing 2 mol% of the LiClO₄ with NaClO₄, then the test described above was repeated. The results were not significantly different from those of curve II of FIG. 2.

From a comparison between curves I and II of FIG. 2, it can be seen that the use of an electrolytic solution containing a suitable amount of Na⁺ ions resulted in a marked improvement in the discoloration efficiency of the EC device, namely by approximately 10% in If the EC device is left in the bleached or colorless state for 1 day and by about 30% for 1 week and by about 50% for 1 month.

Claims (7)

1. Electrochromic device with:
a transparent first substrate covered with a transparent electrode film;
a second substrate which is covered with an electrode film and is arranged opposite and at a distance from the first substrate such that the electrode films on the respective substrates lie opposite one another;
a first electrochromic layer which is applied to the electrode film of one of the substrates and is formed from an electrochromic material which takes on a characteristic color in its electrochemically oxidized state and is selected from the group consisting of Prussian blue, osmium purple and ruthenium purple;
a second electrochromic layer which is applied to the electrode film of the other substrate and is formed from a transition metal oxide from the group consisting of WO₃, MoO₃, V₂O₅, Nb₂O₅ and TiO₂ and mixtures of these oxides with gold, which assumes a characteristic color in its electrochemically reduced state ;
Sealing means for holding the first and second substrates in the opposed and separate arrangement defining a space between the first and second substrates; an auxiliary electrode and an electrolyte solution which fills this space and which contains at least lithium perchlorate or at least sodium perchlorate in an organic solvent, characterized in that the electrolyte solution is a solution of lithium perchlorate and of sodium perchlorate in the organic solvent, the sodium ions 3 to Make up 30 mol% of the total amount of lithium ions and sodium ions. 2. Device according to claim 1, characterized in that the sodium ions in the solution are at least 5 mol% make up the total amount of lithium ions and sodium ions. 3. Device according to claim 2, characterized in that the amount of sodium ions in the solution is not more than 25 mol% of the total amount of lithium ions and is sodium ions. 4. The device according to claim 1, characterized in that the first electrochromic layer ( 24 ) is formed from Prussian blue and that the transition metal oxide is WO₃. 5. The device according to claim 1, characterized in that the organic solvent is propylene carbonate. 6. The device according to claim 1, characterized in that the second substrate ( 10 ) and the electrode film ( 12 ) on the second substrate are transparent. 7. The device according to claim 1, characterized in that that the organic solvent up to 5 wt .-% Water is added.